As the mainstream of an electrophotographic process, there is a xerographic process, which is fundamentally composed of 6 steps. Namely, the xerographic process is generally comprised of 1st step of electrostatically charging a photosensitive member, 2nd step of light-exposing the photosensitive member to form electrostatic latent images, 3rd step of developing the electrostatic latent images of the photosensitive member by applying thereto a toner, 4th step of transferring the developed toner images onto recording paper by utilizing electric field, a 5th step of fixing the toner images transferred onto the recording paper, and a 6th step of cleaning the photosensitive member for removing remaining toners. In a conventional apparatus, the devices for performing the 1st step to the 4th step and the device for performing the 6th step are separately disposed along a drum-form photosensitive member having a relatively large diameter of a sheet-form photosensitive member and the device for performing the 5th step is disposed in the transporting device for recording papers. (See, R. M. Schaffert, "Electrophotography", published by the Focal Press Limited, London and New York).
On the other hand, in Japanese Patent Publication (Unexamined) No. 77,848/81, there is proposed a photosensitive member having a photoconductive layer formed on a transparent electrode layer and an electrophotographic recording apparatus equipped with a counter electrode disposed facing the photosensitive member, a power source for applying an electric potential between the counter electrode and the above-described transparent electrode layer, and a light exposure means for irradiating the photosensitive member from the transparent electrode layer side according to light images. In the system, a previously electrostatically charged toner ribbon and a recording paper are disposed between the above-described photosensitive member and the counter electrode in a superposed state such that the toner ribbon is in contact with the photoconductive layer and light image exposure is performed by the above-described light exposure device. Then, the toner molten in conformity with the light images by the light exposure is transferred onto the recording paper to perform image formation.
According to a known xerographic process, it is necessary to specifically dispose the devices for performing the steps described above around a photosensitive drum or along a photosensitive sheet, and also both an electrostatically discharging step and a cleaning step are inevitable. Thus, the apparatus for the process is complicated and has a large size, which makes it difficult to reduce the thickness or the size of the apparatus. Furthermore, in the xerographic process, the mechanism of a developing device is complicated and also in the developing step, a toner is brought into contact with the surface of the photosensitive member at a high speed and robs the surface thereof, which gives bad influences to the life of the photosensitive member.
Furthermore, in the prior art disclosed in the above-described Japanese patent publication (unexamined), a toner ribbon is superposed on the whole surface of a recording paper in contact relation and hence there is a problem that when the toner at the portions irradiated by light is molten and transferred onto the recording paper, the toner tends to also attach to the peripheral portion of the transferred image to cause so-called ghost.
On the other hand, for solving the problems, in the above-described prior art, the inventors previously proposed a novel electrophotographic process which can greatly reduce the step numbers as described in Japanese Patent Application No. 99,369/85. The electrophotographic process is comprised of the following 4 steps.
(a) 1st step of uniformly attaching a previously charged toner onto the whole surface of a photoconductive layer of a photosensitive member comprising a transparent support having formed thereon successively a transparent electrode layer and the aforesaid photoconductive layer.
(b) 2nd step of irradiating the photosensitive member with light from the transparent support side to reduce the electric resistance of the photoconductive layer at the light-irradiated portions.
(c) 3rd step of injecting electrostatic charge of the opposite polarity to the toner disposed on the light-irradiated portions through the above-described transparent electrode and the photoconductive layer at the above-described light-irradiated portions having reduced electric resistance by the light irradiation.
(d) 4th step of directly transferring the selected toner into which the charge of the opposite polarity has been injected onto a recording paper which is disposed facing the surface of the photoconductive layer.
In the above-described four steps, the step 2, the step 3 and the step 4 substantially simultaneously proceed at a same position.